A variety of processes have been perfected which allow the synthesis of crystalline specimens in the laboratory which, with reference to their mode of application or use, are for all practical purposes indistinguishable from their natural counterparts. It is important to note that such synthetic and natural specimens are members of the same species, and are accordingly identical in their gross physical, chemical and structural properties. The term "synthetic" in the context of this invention therefore does not apply to specimens that are simulants, look-alikes, facsimiles or imitations.
Differentiation between gems of different species or between a gem specimen and a look-alike is readily done. For example, it is relatively easy to distinguish between an authentic ruby gemstone and a similarly cut and colored representative of the so-called garnet or spinel family. There are clear physical and chemical differences that produce macroscopic property differences that can be measured by common laboratory techniques and instruments such as refractometers (measurement of the refractive index), spectrometers, or density determinations and hardness measurements.
Strict identification (distinguishing between species) of gemstones is accomplished relatively easy since members of a species have rather identical nonvarying chemical composition and crystal structures. Since chemical composition and structure determine the physical properties, measurements of such gross physical properties yield the means for identification.
However, differentiation of gemstones of the same species, which differ from each other in origin (i.e., natural from synthetic) but not is gross physical, chemical or structural characteristics, poses a significant problem of a higher order. The finite differences that do exist are submicroscopic in character and occur at a level where atomic and electronic processes find their origin. Only in rare cases will such minor differences readily express themselves externally.
The more closely a growth environment of synthetic gemstones is related to that from which the natural specimens originated, and the closer the process is controlled chemically, physically and thermodynamically, the more readily synthetic specimens will be produced which are virtually impossible to differentiate from the best of their natural counterparts. For example, the best synthetic rubies are for all practical purposes indistinguishable from the best of natural rubies such as those from the Magok area of Burma or other fine specimens from Ceylon or Thailand.
A quality gemstone should be sufficiently beautiful to serve the purpose of personal adornment, and also should be durable to make its display lasting and enduring. This functionality of a gem is of course equally well served by a natural specimen as it is by a synthetic representative of equal beauty. However, there are other characteristics that set the natural specimen apart from the synthetic in the area of rarety, preciousness, authenticity, specific origin, value as an investment commodity and specific cost. In particular, the last two categories make it imperative that instrumented means exist to distinguish between naturals and synthetics. The best of natural stones may fetch prizes up to a thousand times that paid for synthetic specimens.
Synthetic stones have found their way into the channels of trade of natural stones. Exact duplicates of natural stones have been cut from synthetic raw material and have taken the place of previously certified natural materials. Similar exchanges occur with gems in mountings and settings.
At least four different growth processes--flame fusion, fluxed melt growth, hydrothermal techniques and solution growth--are capable of producing gem quality ruby and sapphire stones, and several processes are also known to yield high-quality emeralds. The number of manufacturers using these processes is increasing. Further, the value of colored stones as a trading and investment commodity is growing by leaps and bounds.
With thousands of gems of this type being traded each year, there is a clear need for instrumentation to quickly and efficiently differentiate between the products made by nature and by man.
Standard techniques and devices presently exist for distinguishing between natural and synthetic gemstones. Some of these techniques may be found in textbooks on the transmission of electromagnetic energy, as well as scanning electromicroscopy and light microscopy. These techniques make use of the known fact that synthetic gemstones approach perfection in atomic structure to a far greater extent than their natural counterparts. Several forms of radiation have also been used to directly or indirectly determine structural perfection of materials, including gamma rays, X-rays ultraviolet radiation, electron beams and radiation in the visible part of the electromagnetic energy spectrum. However, all of these approaches involve highly specialized and expensive equipment that require highly specialized training, pose availability problems, are limited by range of applicability and often require destructive specimen preparation. In addition, there are often size, orientation and surface quality requirements of the specimen which cannot be readily met by the product available in the trade.
There is to date no available apparatus which will, in one measurement, differentiate between natural and synthetic gemstones of the same species without regard to their size, shape, clarity, brilliance, morphology, color, cut or degree of finish, and which will do so without recourse to reference books, additional or supplemental measurements, and reliance on individual expertise and experience.